The polyphenylene ether resins (also known as polyphenylenoxide resins) represent a well-known technopolymer family and are characterized by a good combination of thermal, mechanical and electrical properties within a wide temperature range. This combination of properties makes the polyphenylene ether resins suitable for being used in a great variety of appliances by means of injection molding or extrusion techniques.
In spite of these several possible commercial appliances of the polyphenylene ether resins (PPE), their utilization is limited due to their low processability mainly attributable to their low fluidity in the molten state, that can cause some difficulties during the extrusion and injection molding operations.
A further drawback is that the polyphenylene resins have a low resistance to solvents after molding and a low resiliency (IZOD), wherefore the use thereof for certain appliances is furtherly limited.
To obviate these shortcomings it was suggested to mix the polyphenylene ether resins with other polymers, which possess said lacking properties.
Thus, for example, U.S. Pat. No. 3,379,792 suggests to improve the fluidity of the polyphenylene ether resins by adding a polyamide. According to the teachings of this patent, however, the mixes are limited to a polyamide concentration up to 25% by weight; in fact, a higher amount of polyamide involves delamination and a remarkable decay of the other physico-mechanical properties such as resiliency.
Apart from this teaching, it is known in literature that polyphenylene ether resins and polyamide resins are not fully compatible with each other in a wide range of proportions, and that poor properties and phase separation occur when the polyamide amount is rather high.
To obviate this drawback it is known in literature to add to the mixture an additive which is reactive with polyphenylene ether resins and polyamide and which is generally known as compatibilizing agent.
Thus, accordingly to U.S. Pat. No. 4,315,086 and the corresponding European Patent No. 24,120, compositions comprising polyphenylene ether and a polyamide, having superior resilience characteristics and an excellent processability, are prepared by mixing the two polymers in the molten state with 0.01-30% by weight of a compound selected from the group consisting of: a) a liquid diene polymer; b) an epoxy compound and c) a compound having in its molecule both (i) a double ethylenic bond C.dbd.C or a triple bond C.tbd.C, and (ii) a carboxylic, anhydride, amide, imide group, a carboxylic, amino or hydroxyl ester.
Japanese patent publication No. 84/66452 describes similar polymeric compositions prepared by using a polyphenylene ether, which has been pre-treated with one of the above-indicated olefinic compounds a)-c), in the presence of a free radical starter.
However, the resulting compositions do not exhibit an excellent balance of properties and, furthermore, the resilience (impact strength) improvements are not yet sufficient.
With a view to obtaining a further improvement of this characteristic it was proposed, in literature, that a rubber, or an elastomeric polymer having a second order transition temperature (Tg) lower than 1O.degree. C. should be added to the polyphenylene ether -polyamide-compatibilizing agent compositions.
U.S. Pat. No. 4,315,086 proposes, to this purpose, to add natural rubbers, butadiene polymers, butadiene/styrene copolymers, isoprene polymers, butadiene/acrylonitrile copolymers, acrylic esters polymers, ethylene/propylene copolymers, ethylene/propylene/diene terpolymers, etc.
International patent application PCT/US/86/O1511 and U.S. Pat. No. 4,654,405 describe thermoplastic compositions comprising compatibilized polyphenylene ether, polyamide and an impact modifier such as e.g. a polystyrene-polybutadiene-polystyrene three-block copolymer (S-B-S).
International patent application PCT/US/87/00479 describes thermoplastic compositions comprising functionalized polyphenylene ether, polyamide and an impact modifier consisting of a selectively and partially hydrogenated two-block copolymer of the A-B type, wherein block A is a styrene polymer and block B is an ethylene/propylene polymer.
European patent application No. 236,596 describes a polymeric composition comprising a polyphenylene ether, a polyamide, an agent capable of improving the compatibility of the polyamide and of the polyphenylene ether and an agent suited to improve the impact strength of the mix and which can be an ethylene/propylene copolymer or an ethylene/propylene/conjugated diene terpolymer, on which a vinyl monomer having an acid carboxylic group or a derivative thereof or an epoxy group has been grafted.
Laid-open European patent application No. EP-A-270246 describes a thermoplastic composition based on a polyphenylene ether and a polyamide containing from 5 to 100 parts, calculated on 100 parts of the mix, of a copolymer consisting of an ethylene/alpha-olefin rubber-like copolymer, an alkenyl aromatic compound and an unsaturated carboxylic acid or an anhydride thereof, which not only is compatible with the composition of the two polymers, but also causes a remarkable improvement of the impact strength. To this end, the presence of the unsaturated carboxylic acid or of its anhydride is considered, in said patent, as absolutely necessary.
The compositions so obtained, however, do not exhibit a best property combination for all the uses they are intended for.
In particular, the presence of the unsaturated carboxylic acid or of its anhydride, grafted on the ethylene/alpha-olefin rubber-like copolymer, improves the compatibility, but to the prejudice of the impact strength, which decreases as the amount of said acid or grafted anhydride increases.